Potentiometer with embedded reversely bent contact wires

ABSTRACT

Miniature potentiometer of such small dimensions that resistance element and contact dimensions are so reduced as to create severe problems in respect to high contact-resistance-variation, wherein contact-resistance-variation is grossly minimized by employing as a contact device for brushing and bridging the resistance element and a return conductor or bus a set of very small-gauge resilient wires arranged in side-by-side ribbonlike configuration with central portions embedded in a rotor member and end portions reversely bent to form a number of resilient independently movable spring contacts disposed to brush a series of closely spaced points along a line transverse of the resistive element. Thus the contact pressure is not concentrated at a single point but at a maximum number of points, reducing contact wear and electrical contact-resistance-variation.

United States Patent Inventor Robert D. Michik Riverside, Calif.

Appl. No. 789,108

Filed Jan. 2, 1969 Patented Apr. 27, 1971 Assignee Bourns, Inc.

POTENTIOMETER WITH EMBEDDED REVERSELY BENT CONTACT WIRES 8 Claims, 9Drawing Figs.

US. Cl 338/202, 338/171 Int. Cl 1101c 1/12, HOlc 5/02 field ofSearch338/(screw digest), 162, 163, 166, 171, 174, 183, 202; 200/ 166 (B8)References Cited UNITED STATES PATENTS 3,274,368 9/1966 DeBoo 29/630Primary Examiner-Lewis l-l. Myers Assistant Examiner-Gerald P. TolinAtt0meyFritz B. Peterson ABSTRACT: Miniature potentiometer of such smalldimensions that resistance element'and contact dimensions are so reducedas to create severe problems in respect to highcontact-resistance-variation, wherein contact-resistance-variation isgrossly minimized by employing as a contact device for brushing andbridging the resistance element and a return conductor or bus a set ofvery small-gauge resilient wires arranged in side-by-side ribbonlikeconfiguration with central portions embedded in a rotor member and endportions reversely bent to form a number of resilient independentlymovable spring contacts disposed to brush a series of closely spacedpoints along a line transverse of the resistive element. Thus thecontact pressure is not concentrated at a single point but at a maximumnumber of points, reducing contact wear and electricalcontact-resistance-variation.

POTENTIOMETER WITH EMBEDDED REVERSELY BENT CONTACT WIRES BACKGROUND OFTHE INVENTION Increasing complexity of electronic circuitry, togetherwith increasing usage of electronic-circuit components in environmentssuch as satellite and like vehicles, wherein reduction of occupied spaceand of weight are of prime importance, has intensifred the need forsmaller, lighter and simpler components. Mere scalar reduction of sizewhereby to attain the noted ends can be carried on only to a limitedextent. Therebeyond, further reduction results in parts failure,excessive wear, unacceptable electrical capacity and/or performance, andother undesirable results. Among the latter, in the case ofpotentiometers, is unacceptably high variation of contact resistance;that is, change of resistance exhibited between a resistance element andthe movable contact at the region of contact therebetween. Thatvariation of resistance is termed contactresistance-variation,abbreviated CRV. As the physical sizes of the resistance element and themovable contact or wiper of a potentiometer are reduced, the pressureforce required to attain a reasonably low value of contact resistance(CR) increases and thus unacceptable excessive wear of the contactoccurs. This effect is aggravated in the case of cermet resistanceelements, which tend to be more abrasive than carbon or compositionelements. One expedient to which resort has been taken to alleviate theproblem of high CRV and excessive wear due to high contact pressureforce has been to divide the contact into several fingers or limbs, eachof which serves as an independently sprung contact and which fingersthus multiply the number of areas or regions of contact and concurrentlyreduce the individual contact force required and, hence, the CRV.However, slitting or punching of a thin sheet of metal to producemultiple fingers becomes an exorbitantly expensive operation when thestrip dimensions become small. For example, to provide four fingers atthe end of a strip onesixteenth inch wide, requires clean and accurateparting offingers one-sixty-fourth inch wide. Die means to'perform suchan operation, even in seriatim, are very expensive and of short lifeduration. Further, such sheared or slit-strip contacts often arenonuniform in action, that is, successive ones of a group thereof varywidely in contact resistance and in CRV during operation; suchvariability probably being the result of interfering burrs alongadjacent sheared edges of the fingers. It is of great importance, in themanufacture and sale of potentiometers, that the importantcharacteristics of all potentiometers of a manufactured class be asnearly uniform or alike as possible. When CRV and like characteristicsvary from potentiometer to potentiometer among a group of supposedlyidentical potentiometers, the sales quality is downgraded; hence it ishighly desirable that CRV be uniform from one potentiometer to anotherin the same group or class, and that it be as low in value as possible.

SUMMARY OF THE INVENTION utilizing a set of very closely spacedfine-gauge wires arranged in a sheetlike or ribbon formation and doublybent as a group whereby one end of each wire is disposed to wipe arespective one of points dispersed transversely across a resistanceelement. Preferably, also, the other end of each wire contacts and wipesa return conductor. The wires as a group are held in place inside-by-side disposition by having an intermediate portion of the wireembedded in an insulative wiper block or carrier. Further, the wires areso bent, adjacent each exit from the embedment, that the middle portionof each wire is torsionally stressed, whereby the force with which eachwire presses its contacting end against the resistance element is not,as is usual in potentiometer contacts, the result of unbalancedcompression-tension strains such as are experienced by a stressed leafspring. Because of the utilization of torsional stressing of the wiresof the contact, the lengths of the wires can be greatly reduced with nodetrimental increase in the- DESCRIPTION OF THE DRAWINGS The presentlypreferred exemplary embodiment of the invention is illustrated in thedrawings comprised in this description, in which drawings:

FIG. 1 is an enlarged pictorial view of a single-tum rotarypotentiometer, comprising a rotor carrying a contact device, embodyingthe principles of the invention;

FIG. 2 is a grossly enlarged sectional view in elevation of thepotentiometer shown in FIG. 1;

FIG. 3 is a view in elevation of the contact device and actuator orrotor, of the exemplary potentiometer depicted in section in FIG. 2

FIG. 4 is a bottom view of the structure shown in elevation in FIG. 3;

FIG. 5 is a bottom view of the device shown in FIGS. 3 and 4, prior tobending of the contact wires;

FIG. 6 is a sectional view of the rotor and contact wires depicted inFIGS. 4 and 7, the section being as indicated by indicators 6-6 in FIG.5;

FIG. 7 is a top view of the device shown in FIGS. 3 and 4, prior tobending of the contact wires;

FIG. 8 is a top plan view of a potentiometer base comprised in thepotentiometer depicted in FIG. 1, the base comprising an insulativeplate, terminal pins or wires, conductive means, and a resistive trackor element; and

FIG. 9 is a bottom plan view of the base shown in FIG. 8.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT OF THE INVENTION The inventionis for convenience illustrated herein as being comprised in a very smallminiature potentiometer of the single-turn rotary class, but it will beevident to those skilled in the resistor art that the principles of theinvention are equally applicable to other types of potentiometers,including lead screw adjusted potentiometers. The illustrativepotentiometer is of the order of 6 millimeters diameter as commerciallyproduced. The potentiometer, labeled 10 as a unit (FIGS. 1 and 2)comprises a support means in the form of an insulative baseplate 12,preferably of alumina or steatite, a contact carrier in the form of arotary means comprising an insulative rotor 14, a contact means carriedby the carrier, and ametal cap 16 which serves to provide an operatingchamber A above the plate and to confine the rotor torotary movements inthe chamber. The baseplate 12 has embedded therein portions .ofterminals T1, T2 and T3 (FIG. I) of wire, the upper ends of theterminals being accessible at the upper to top face of plate 12 asindicated in FIG. 9.

Bridging the upper exposed ends of terminals T1 and T3 and adherent onthe upper face of the plate is a flat resistive element E (FIG. 8) ofresistive material such as cermet, the ends of which element areconductively connected to the noted terminals by conductive paint P asis or may be customary in modern resistor manufacture. A centrallydisposed conductor or collector, C, is similarly adherent upon the uppersurface of baseplate l2 and is directly connected to the terminal T2 asis indicated in FIG. 2. The baseplate is provided with threespaced-apart notches N1, N2 and N3 FIG. 9), for reception ofcomplementary tabs such as I6! (FIG. 2) provided along the lower edge ofcap I6, whereby the cap is retained to the base plate I2.

The rotor 14 is confined in the chamber A by the baseplate l2 and theinwardly extending flange 16f (FIG. ll) of the cap which overlies theperiphery of the upper or top surface of the body of therotor. The rotorcomprises an operator in the form of an upwardly extending formation14/: (FIG. 2) which is provided with a driver-receiving slot Mt (FIG.'7). The formation 14h extends through the upper aperture of the cap 16;and the rotor, being of round configuration, is journaled in theencircling cylindrical body of the cap. The inwardly directed flange ofcap 16 is extended inwardly to form a 7) lbs (FIGS. 1 and 2) forcoaction with a complementary stop 14s (FIGS. 2 and 7) in the form of anabutment or protuberance formed on the upper face of rotor 14, wherebyrotation of the rotor is restricted to somewhat less than 360 ofrotation in either direction.

On its bottom face the rotor 14 is formed to provide a plurality ofdownwardly extending pluglike protuberances 14a,

14b, 14c and [4d (FIGS. 4) and 5), and first and second depressions Meand 14f separated by a beveled portion 14g the principal surface ofwhich is generally coplanar with that of the lower face of the main bodyof the rotor. Embedded in the rotor as a side-by-side ribbonlike sheetis the intermediate length of a plurality of set of very fine-gaugewires W (FIGS. 2

- and 3). The sheet or set of wires W is initially straight, asindicated in FIGS. 5 and 7, lying flat against the surface of the bodyof the rotor at the base of the depressions Me and 14f, and extendingthrough the body of the rotor between the depressions, as indicated bydotted lines in FIG. 5. During manufacture of the contact carriers, thecontact wires W are drawn from spools through guide and tensioning meansinto parallel side-by-side flat ribbonlike formation, through moldingmachinery which molds onto the ribbon of wires a continuing series ofspaced-apart contact carriers (here, rotors), and on through machinerywhich severs the ribbon of wires between successive rotors, clamps thesevered unit, and reversely bends and offsets the wires as a sheet orunit into the configuration illustrated in FIG. 4. Thus the short ribbonof parallel wires W, with first and second ends Wu and Wb, respectively,as shown in FIG. 5, is reversely bent at locations Wv and Wx asindicated in FIG. 3, and laterally offset as indicated in FIG. 4 toposition the ends Wa between two of the protuberances 14b and 14d andthe ends Wb between protuberances 14a and 14b. The protuberances servethe dual functions of preventing undersired lateral splaying orspreading of the wires when the ends are stressed in brushing theresistive element or collector, and of contacting the surface of thebasesupported components and thereby establishing a predeterminedminimum spacing of the rotor from the baseplate and a detennined maximumstressing of the contact wires.

As has been made clear, the contact wires at ends Wb are laterallyoffset when reversely bent, and the wires are at ends Wa laterallyoffset in the opposite direction. Valuable results are attained by sobending and offsetting the wire ends, in addition to the large savingsin manufacturing (fabricating) and material costs. First, anexceptionally compact contact-carrier and contact-spring arrangement isattained, Secondly, a maximum number of fully independent contact areasbrushing the resistance element is provided, Thirdly, by offsettingeither of the ends and thus torsionally stressing the wires, muchgreater contact pressure is attained in a resilient contact than isattainable in a cantilever-type spring contact. This advantage is ofcritical importance in potentiometers of very small dimensions, since itallows the individual contact members a considerable measure ofresilience while they press against the resistive element with therequisite force. If a relatively nonresilient contact member having thesame contact-area brushes the element with the same force, it would witha high degree of probability dig into the element and rapidly destroythe usefulness of the potentiometer.

The use of contact wires of round or oval cross section permits thecontact members to be crowded together in side-byside contactingrelationship without either thereof interfering with any other in theirslight relative movements during brushing of the element and collectorsurfaces. Such permitted and desirable relative movement is as apractical matter substantially impossible of attainment withsheared-sheet contact members without splaying or spreading the contactswith resultant loss of effective contact area, because of theinteraction of minute burrs along the adjacent sheared edges of thecontact fingers.

Sealing of the potentiometer is accomplished by conventional O-ringmeans (not shown) and sealant (not shown) applied around the lowerjuncture of the cap and baseplate, both of which means are conventionalin the art and neither of which is, per se, of the present invention.

I claim:

1. In a potentiometer,

support means for supporting a substantially flat elongate resistiveelement an exposed surface of which provides a resistive track to bebrushed, and such a resistive element thereon, with terminals at eachend thereof;

conductive means including collector means and a terminal therefor;

a contact carrier and contact means carried by said carrier,

said contact means comprising a ribbonlike array of individual elongatewires in side-by-side relationship throughout their lengths, each ofsaid wires having an intermediate straight portion in substantiallyplanar disposition with the others of said wires and all of theintermediate straight portions of said wires being embedded in saidcarrier and all of said wires having first end portions reversely bentclosely adjacent to said embedded portion and laterally offset from saidstraight portions thereof to provide at the first ends of said wiresrespective contact areas brushing on said resistive element, the secondend portions of said wires being similarly but oppositely reversely bentand oppositely offset relative to said straight portions and having atthe ends thereof respective contacts brushing on said conductive means,at least said first end portions being torsionally stressed; and

means coacting with said support means to retain said carrier inposition with the contact areas of said contact means in brushingrelation to said element;

whereby said contact means provides aplurality of individually sprungresilient torsionally stressed wires presenting contacts inside-by-side. closely spaced relationship to greatly minimizecontact-resistance-variation as said element is brushed by said contactmeans.

2. Potentiometer means as defined by claim 1, in which said collectormeans is a conductive member having a flat surface, and in which thesecond end of each of said wires comprises a contact area brushing onsaid conductive member.

3. Potentiometer means as defined in claim 2, in which said second endportions of said wires are closely adjacent to said embedded portion,whereby said contact areas on said second ends of said wires are closelyadjacent to the contact areas of said first ends of said wires, wherebyan extremely compact contact construction occupying a minimum of spaceis provided.

4. Potentiometer means as defined by claim 3, in which said contactcarrier comprises protuberances extending therefrom and betweenrespective pairs of opposed surfaces of which protuberances the saidfirst ends and the said second ends of said wires as groups extend,whereby the ribbonlike ends of said wires receive lateral support sothat the ends to not splay or spread when brushing on said element.

5. A single-tum miniature potentiometer comprising:

first means, including housing means forming an enclosure,

a resistive element and a conductive element disposed in the enclosure,and terminal connections to said elements extending therefrom to theexterior of the housing means, said resistive element being an arcuatemember having a substantially flatexposed surface disposed around anaxis defined by said housing means;

second means, including rotary means comprising a rotor rotatable aboutsaid axis and having means for effecting rotation thereof, said rotorhaving aportion confined in said enclosure by said housing means forrotation about saidaxis;and' W third means, including a plurality ofelongate fine-gauge contact wires arranged in side-by-side ribbonlikearray with first and last wires of the array confined at the edges ofthe array by means included in said second means, said wires as a grouphaving a central portion thereof embedded in and firmly integrated withsaid rotor and having a first end portion thereof reversely bent andextending away from said rotor into side-by-side brushing engagementwith said arcuate element and said wires as a group having the secondend portion thereof reversely bent and extending away from said rotorinto brushing contact with said conductive element;

whereby aid reversely bent end portions of said group of wires provide aplurality of resilient brushing contacts in side-by-side contactingrelationship to minimize contactresistance-variation.

6; A miniature potentiometer according to claim 5, in which said rotorcomprises spaced-apart protuberances between which said ribbonlike arrayof wires extends and by which they are restrained from laterallyseparating.

7. A miniature potentiometer according to claim 5, in which each endportion of said group of wires in ribbonlike array is laterally offsetfrom said central portion as well as reversely bent, ,whereby individualwires are subjected to torsional stress as well as compressive stress.

8. In a potentiometer,

support means for supporting a substantially flat elongate resistiveelement an exposed'surface of which provides a resistive track to bebrushed, and such a resistive element thereon, with terminals at eachend thereof;

conductive means including collector means and a terminal therefor;

a contact carrier and contact means carried by said carrier,

said contact means comprising a ribbonlike array of individual elongatewires in side-by-side relationship throughout their lengths, each ofsaid wires having an embedded portion embedded in said carrier andhaving at least a first end thereof reversely bent closely adjacent tosaid embedded portion to provide at the said one end a contact areabrushing on said resistive element, the contact areas of at least someof said wires brushing said element along a line transversely of saidtrack, and at least some of the ends of said wires contacting saidconductive means; and

means coacting with said support means to retain said carrier inposition with said contact means in brushing relation to said element;

whereby said contact means provides a plurality of individually sprungresilient contacts in side-by-side closely spaced relationship togreatly minimize contact-resistance-variation as said element is brushedby said contact means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,576,514 Dated pril 27, 1971 Inv Robert D. Michik It is certified thaterror appears in the above iden tified atent and that said LettersPatent are hereby corrected as shown below? Column 3 line 10 "7)" shouldread stop Column 5 line 16, "aid" should read said Signed and sealedthis 30th day of November 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Pate

1. In a potentiometer, support means for supporting a substantially flatelongate resistive element an exposed surface of which provides aresistive track to be brushed, and such a resistive element thereon,with terminals at each end thereof; conductive means including collectormeans and a terminal therefor; a contact carrier and contact meanscarried by said carrier, said contact means comprising a ribbonlikearray of individual elongate wires in side-by-side relationshipthroughout their lengths, each of said wires having an intermediatestraight portion in substantially planar disposition with the others ofsaid wires and all of the intermediate straight portions of said wiresbeing embedded in said carrier and all of said wires having first endportions reversely bent closely adjacent to said embedded portion andlaterally offset from said straight portions thereof to provide at thefirst ends of said wires respective contact areas brushing on saidresistive element, the second end portions of said wires being similarlybut oppositely reversely bent and oppositely offset relative to saidstraight portions and having at the ends thereof respective contactsbrushing on said conductive means, at least said first end portionsbeing torsionally stresSed; and means coacting with said support meansto retain said carrier in position with the contact areas of saidcontact means in brushing relation to said element; whereby said contactmeans provides a plurality of individually sprung resilient torsionallystressed wires presenting contacts in side-by-side closely spacedrelationship to greatly minimize contact-resistance-variation as saidelement is brushed by said contact means.
 2. Potentiometer means asdefined by claim 1, in which said collector means is a conductive memberhaving a flat surface, and in which the second end of each of said wirescomprises a contact area brushing on said conductive member. 3.Potentiometer means as defined in claim 2, in which said second endportions of said wires are closely adjacent to said embedded portion,whereby said contact areas on said second ends of said wires are closelyadjacent to the contact areas of said first ends of said wires, wherebyan extremely compact contact construction occupying a minimum of spaceis provided.
 4. Potentiometer means as defined by claim 3, in which saidcontact carrier comprises protuberances extending therefrom and betweenrespective pairs of opposed surfaces of which protuberances the saidfirst ends and the said second ends of said wires as groups extend,whereby the ribbonlike ends of said wires receive lateral support sothat the ends to not splay or spread when brushing on said element.
 5. Asingle-turn miniature potentiometer comprising: first means, includinghousing means forming an enclosure, a resistive element and a conductiveelement disposed in the enclosure, and terminal connections to saidelements extending therefrom to the exterior of the housing means, saidresistive element being an arcuate member having a substantially flatexposed surface disposed around an axis defined by said housing means;second means, including rotary means comprising a rotor rotatable aboutsaid axis and having means for effecting rotation thereof, said rotorhaving a portion confined in said enclosure by said housing means forrotation about said axis; and third means, including a plurality ofelongate fine-gauge contact wires arranged in side-by-side ribbonlikearray with first and last wires of the array confined at the edges ofthe array by means included in said second means, said wires as a grouphaving a central portion thereof embedded in and firmly integrated withsaid rotor and having a first end portion thereof reversely bent andextending away from said rotor into side-by-side brushing engagementwith said arcuate element and said wires as a group having the secondend portion thereof reversely bent and extending away from said rotorinto brushing contact with said conductive element; whereby aidreversely bent end portions of said group of wires provide a pluralityof resilient brushing contacts in side-by-side contacting relationshipto minimize contact-resistance-variation.
 6. A miniature potentiometeraccording to claim 5, in which said rotor comprises spaced-apartprotuberances between which said ribbonlike array of wires extends andby which they are restrained from laterally separating.
 7. A miniaturepotentiometer according to claim 5, in which each end portion of saidgroup of wires in ribbonlike array is laterally offset from said centralportion as well as reversely bent, whereby individual wires aresubjected to torsional stress as well as compressive stress.
 8. In apotentiometer, support means for supporting a substantially flatelongate resistive element an exposed surface of which provides aresistive track to be brushed, and such a resistive element thereon,with terminals at each end thereof; conductive means including collectormeans and a terminal therefor; a contact carrier and contact meanscarried by said carrier, said contact means comprising a ribbonlikearray of individual elongate wires in side-by-side relationshipthroughout their lengths, each oF said wires having an embedded portionembedded in said carrier and having at least a first end thereofreversely bent closely adjacent to said embedded portion to provide atthe said one end a contact area brushing on said resistive element, thecontact areas of at least some of said wires brushing said element alonga line transversely of said track, and at least some of the ends of saidwires contacting said conductive means; and means coacting with saidsupport means to retain said carrier in position with said contact meansin brushing relation to said element; whereby said contact meansprovides a plurality of individually sprung resilient contacts inside-by-side closely spaced relationship to greatly minimizecontact-resistance-variation as said element is brushed by said contactmeans.